The present invention relates to computer input devices, such as mice and trackballs. In particular, it relates to the reduction of the number of components and improvements in tracking performance.
Typically, such input devices have a ball which is rolled when a user moves the mouse across the desktop, or is manipulated with the user""s finger for a trackball. The ball is in frictional contact with various rollers. The ball""s motion is detected by two rollers that are offset from each other at an angle of 90 degrees. These two rollers which rest against the ball detect the ball""s motion in the x and y directions respectively. Each roller is typically connected to an encoder disk via a shaft, with the combination of the roller, shaft and encoder disk referred to as a xe2x80x9cCombiDisk.xe2x80x9d Each encoder disk has radial slits, which when used in conjunction with a photo emitter and a photo detector allow for the determination of the amount of movement of the ball in the x or y directions. A pressure roller is provided, which is spring biased to provide a force to keep the ball engaged with the rollers of the CombiDisks. Typically designs use anywhere from one to three pressure rollers which are spring biased and provide improved shock loading. The ball rests against the pressure roller(s) and thus does not frictionally engage the cavity in the outer housing of the input device.
One of the challenges in the design of such input devices is the reduction of costs. In the extremely competitive input device market, savings of pennies are very significant. One method to reduce costs is to simplify the design and reduce the number of components required to the build the input device.
Another challenge in the design of such devices is tracking precision. Typical CombiDisks comprising cylindrical rollers, shafts, and encoder disks are held in place on axial supports, and are susceptible to axial play when the direction of movement changes. Axial play is the CombiDisk""s axial translation with respect to its supports which is induced by the movement of the ball in a direction parallel to the axis of the CombiDisk. Typically, as the input device is moved, the ball gets rolled, and frictional forces drag the roller and hence the CombiDisk in the direction of the movement of the input device. Once the direction of the movement of the input device is changed, the CombiDisk xe2x80x9cplaysxe2x80x9d in the changed direction. This axial play adversely impacts the tracking precision of such input devices. The shaft""s longitudinal play also adds tolerances and requirements to the optical detection system to make the system insensitive to the variations of position of the disk relative to the photo emitters and detectors.
The present invention provides a method and apparatus for replacing two separate photo detector chips and two photo emitters by a single photo detector chip and a single photo emitter. This is achieved by using CombiDisks having a flexible shaft. The flexible section allows for the bending of the CombiDisks so that the encoder disks are next to each other and tangent to the same vertical plane. This allows for the placement of both the x and the y sensors in a single plane. This will in turn allow for the two photo detectors to be integrated in a single semiconductor chip, saving a separate photo detector chip, and its associated packaging. This additional savings is significant since the packaging itself contributes to approximately one half of the cost of such a detector.
The middle section of the CombiDisk is made of a highly flexible material such as spring steel, and is bent to create a spring force. This bending causes the CombiDisks to exert a spring force against the ball and hence eliminates the need to have a spring-biased pressure roller. The prior art spring-biased roller can now be replaced with a simple roller, eliminating a spring and the associated spring-bias linkage and assemblies, and hence provide for another cost savings.
The rollers on the CombiDisks in one embodiment of the present invention are conical. The conical rollers are tapered away from the encoder disks creating a ramp-like body causing the ball to want to move away from the encoder disks. Accordingly, the equal and opposite reactive force tends to move the conical roller towards the encoder disks. Since the rollers are rigidly attached to the encoder disks via a bent flexible shaft, the force created by the ball on the roller tends to push the encoder disk away from the ball. As such, the role of the conical rollers is to impart a compressive force along their axis of rotation. This force also ensures the encoder disk is always pressed against the axial stop, making the position of the disk more precise and not subject to axial play when the direction of the movement is changed.
In a preferred embodiment, CombiDisks contact the ball at 90 degrees. Each CombiDisk is comprised of a bent flexible steel shaft connecting a conical roller on one end to the encoder disk on the other. The two conical shaped rollers have a cone angle in the range of zero to 45 degrees, which is a function of the ball""s size, and are biased against the ball, with the vertex of the cone opposite to the encoder disk. A third roller, in contact with the ball, is placed equidistant from the CombiDisk rollers and on the opposite side of the ball from the encoder disks. The semiconductor chip with the photo detectors is mounted vertically on one side, and the photo emitters are mounted vertically on the other side of the encoder disks.